Issue with Content Type Required field

Recently while creating a custom content type feature, I realized the fields are coming as Optional even after setting attribute Required = “true”

<FieldRef ID="{3154C55D-956E-4049-831F-39AFF3AB7787}" Name="Patient" Required="true" ShowInDisplayForm="true" ShowInNewForm="false" ShowInEditForm="true" />

After changing the attribute value to TRUE (uppercase), Content type fields worked fine.

<FieldRef ID="{3154C55D-956E-4049-831F-39AFF3AB7787}" Name="Patient" Required="TRUE" ShowInDisplayForm="TRUE" ShowInNewForm="FALSE" ShowInEditForm="TRUE" />